In mobile phones, the strength of the received signal strength indicator (“RSSI”) is displayed to the user on the screen. The display is normally in the form of an RSSI icon. The RSSI icon is modified whenever the received signal changes in level, for example when it rises or falls beyond predefined levels. This may be done by changing the number of bars or height of a bar in the RSSI icon.
A dual mode or WiFi enabled phone has two microprocessors, one for the cellular network which may be a code division multiple access (“CDMA”), frequency division multiple access (“FDMA”), or time division multiple access (“TDMA”) processor, for example, and the other for the wireless local area network (“WLAN”). A dual mode cellular and WiFi phone, for example a CDMA+WiFi phone, needs to display the RSSI icon based on the access technology which is in use by the user at the moment. If the phone is using a cellular phone technology such as CDMA, TDMA, or the like, i.e. the user is making or receiving telephone calls over a cellular data network, the CDMA microprocessor displays the signal strength received from the cellular base station. If the phone is using another wireless network, such as a wireless local area network or WiFi network, either to send or receive data or to make or receive calls over the WiFi network, the screen must display the signal strength received from the associated access point of the wireless network.
In a typical system, the cellular or CDMA microprocessor monitors and processes the received signal strength of the cellular base station, while the WiFi microprocessor monitors the received signal strength of the associated access point. However, since the display of the RSSI icon is controlled by the cellular microprocessor, it must obtain the WiFi received signal strength from the WiFi microprocessor. The cellular microprocessor therefore queries the received signal strength of the WiFi signal periodically, using the interface between the two microprocessors. If the signal strength reduces below a certain threshold, the cellular or CDMA microprocessor performs certain actions related to seamless mobility, and also uses this information to update the RSSI icon.
The CDMA and WiFi microprocessors communicate with each other using messages. A timer in the CDMA microprocessor is used to determine the time interval between signal strength queries being sent to the WiFi microprocessor. On receipt of the query, the WiFi microprocessor calculates the RSSI and prepares a response message, which is then sent from the WiFi microprocessor to the CDMA microprocessor. If there has been any change in the WiFi received signal strength since the previous RSSI response message, the RSSI icon is updated to reflect the current received signal strength, and the CDMA microprocessor performs other actions if required for seamless mobility, for example if the received signal strength has fallen below a threshold.
In this system, the CDMA microprocessor has to send requests to the WiFi microprocessor periodically to receive the current WiFi received signal strength. This requires a relatively large number of messages back and forth between the two processors, reducing battery life. It also places an extra burden on the WiFi processor, which must send a current RSSI message to the CDMA microprocessor every time a query is received, regardless of whether the signal strength has changed.
Therefore, what is needed is a system and method that reduces the number of back and forth messages required for the cellular microprocessor to update the RSSI icon when the phone is operating in the WiFi mode.